Plastic has taken the place of other materials in a variety of industries. Because plastic can be engineered to not shatter, rust or rot, plastic articles have replaced glass, metal and wood articles in many applications. For example, in the food and packaging industries, plastic has replaced glass to minimize breakage, reduce weight, and reduce energy consumed in manufacturing and transport.
Additives are often added to a plastic to facilitate the processing of that material. Commonly used additives are slip agents, which act as an internal lubricant for the polymer during processing. For instance in film processing, slip additives lessen friction between the polymer film and high speed processing and packaging equipment.
Slip additives often function by migrating (i.e. “blooming”) to the surface of the polymer, where they provide a coating that reduces the surface's coefficient of friction. Because the additive is concentrated at the surface where it is needed for processing, less slip additive is required in the polymer material overall.
Typically variants of fatty acids are used as slip additives, because they are immiscible within, and chemically inert to, the polymer matrix, making them more likely to be migratory. For example, many commonly used slip additives, such as erucamide, oleamide, stearamide, behenamide, oleyl palmitamide, stearyl erucamide, ethylene bis-oleamide, N,N′-Ethylene Bis(Stearamide) (EBS), are highly migrant (i.e. migration occurs within hours of the film formation).
However, there is also loss of slip additive, due to additive migration or transfer from the polymer material. “Additive migration” represents the slip additive migrating from the sliding layer of the film containing slip additive, to another film layer. “Additive transfer” represents the slip additive transferring to another substrate (for example transferring to another section of the film when it is rolled). Therefore, films and other articles with migratory slip additives experience diminished slip properties over time or exposure to higher temperatures.
Consequently, if for example there is an interval before further processing, those polymer materials containing traditional migratory slip additives may require cold storage. Slip performance may also decrease when exposed to high processing temperatures. Finally, migratory slip additives are not suitable for applications that require consistent slip properties over the useful life of the article, such as for release films and permanent anti-slip coatings.
High molecular weight (HMW) non-reactive silicone gums have been found to migrate more slowly (over days versus hours). However, the trade off is reduced slip properties, represented by higher COF values, and limited long-term stability.